Region-of-interest biased tone mapping

Abstract

Methods, devices and computer readable instructions to generate region-of-interest (ROI) tone curves are disclosed. One method includes obtaining a statistic for an entire image such as, for example, a luminance statistic. The same statistic may then be found for a specified ROI of the image. A weighted combination of the statistic of the entire image and the statistic of the ROI yields a combined statistic which may then be converted to a ROI-biased tone curve. The weight used to combine the two statistics may be selected to emphasize or de-emphasize the role of the ROI's statistic in the final tone curve.

The invention claimed is: 
     
       1. A method to process an image, comprising:
 obtaining a first image of a scene from a memory; 
 obtaining a first statistic of an entirety of the first image; 
 identifying a region-of-interest (ROI) of the first image, wherein the ROI comprises less than the entirety of the first image; 
 obtaining the first statistic of the ROI of the first image; 
 determining a single tone curve for the first image that is ROI-biased based on a weighted combination of the first statistic of the entirety of the first image and the first statistic of the ROI of the first image; 
 applying the single tone curve to a second image to generate a tone-mapped image; and 
 storing the tone-mapped image in the memory. 
 
     
     
       2. The method of  claim 1 , wherein the first statistic comprises a statistic based on image luminosity. 
     
     
       3. The method of  claim 1 , wherein obtaining a first image comprises:
 obtaining from a camera's image sensor, a pre-image; and 
 displaying the pre-image on a display element of the camera. 
 
     
     
       4. The method of  claim 3 , wherein identifying a region-of-interest (ROI) comprises:
 receiving an input from the display element indicative of an area of the display element; 
 translating the indicated area of the display element to a corresponding area of the pre-image; and 
 identifying the corresponding area of the pre-image as the ROI. 
 
     
     
       5. The method of  claim 4 , wherein the display element comprises a touch-sensitive display element. 
     
     
       6. The method of  claim 3 , wherein applying the single tone curve to a second image comprises:
 receiving a capture command from the camera; 
 obtaining the second image from the camera's image sensor in response to the capture command; and 
 applying the single tone curve to the second image to generate the tone-mapped image. 
 
     
     
       7. The method of  claim 6 , further comprising displaying the tone-mapped image on the display element. 
     
     
       8. An image capture device, comprising:
 an image sensor; 
 a memory operatively coupled to the image sensor and having stored therein processor-executable instructions; 
 a display operatively coupled to the memory; and 
 one or more processors operatively coupled to the image sensor, the memory and the display, wherein the one or more processors are programmed to execute the processor-executable instructions and, in response thereto—
 obtain a pre-image of a scene from the image sensor; 
 obtain a first statistic of an entirety of the pre-image; 
 display the pre-image on the display; 
 receive an input that identifies a region-of-interest (ROI) of the pre-image, wherein the ROI comprises less than the entirety of the pre-image; 
 obtain a first statistic of the ROI of the pre-image; 
 determine a weighted combination of the first statistic of the entirety of the pre-image and the first statistic of the ROI to generate a ROI-biased first statistic; 
 determine a single tone curve based on the ROI-biased first statistic; 
 obtain a first image of the scene from the image sensor; 
 apply the single tone curve to the first image to generate a second image; and 
 store the second image in the memory. 
 
 
     
     
       9. The image capture device of  claim 8 , wherein the first statistic comprises a statistic based on luminosity. 
     
     
       10. The image capture device of  claim 8 , wherein when the one or more processors execute the instructions to identify a ROI of the pre-image, the one or more processors:
 receive an input indicative of an area of the display; 
 translate the indicated area of the display to a corresponding area of the pre-image; and 
 identify the corresponding area of the pre-image as the ROI. 
 
     
     
       11. The image capture device of  claim 10 , wherein the display comprises a touch-sensitive display. 
     
     
       12. The image capture device of  claim 8 , wherein when the one or more processors execute the instructions to generate the ROI-biased first statistic, the one or more processors combine the first statistic of the ROI (X) and the first statistic of the entirety of the pre-image (Y) as follows: (ROI-biased first statistic)=wX+(1−w)Y, where ‘w’ represents a weight value. 
     
     
       13. The image capture device of  claim 8 , wherein when the one or more processors execute the instructions to obtain a first image, the one or more processors:
 receive a capture command from the image capture device; 
 cause, in response to the capture command, the image sensor to capture the first image. 
 
     
     
       14. A non-transitory program storage device comprising instructions stored thereon to cause one or more processors to:
 obtain a first image of a scene; 
 obtain a first statistic of an entirety of the first image; 
 identify a region-of-interest (ROI) of the first image, wherein the ROI comprises less than the entirety of the first image; 
 obtain a first statistic of the ROI of the first image; 
 determine a single tone curve for the first image that is ROI-biased based on a weighted combination of the first statistic of the entirety of the first image and the first statistic of the ROI; 
 obtain a second image of the scene; 
 apply the single tone curve to the second image to generate a third image; and 
 store the third image in a memory. 
 
     
     
       15. The non-transitory program storage device of  claim 14 , wherein the instructions to cause the one or more processors to obtain a first image comprise instructions to cause the one or more processors to:
 obtain a pre-image of the scene from an image sensor of an image capture device; and 
 display the pre-image on a touch-sensitive display of the image capture device. 
 
     
     
       16. The non-transitory program storage device of  claim 15 , wherein the instructions to cause the one or more processors to obtain a first statistic of the entirety of the first image comprise instructions to cause the one or more processors to obtain a statistic based on the first image's luminosity. 
     
     
       17. The non-transitory program storage device of  claim 16 , wherein the statistic based on luminosity comprises a luminosity histogram. 
     
     
       18. The non-transitory program storage device of  claim 15 , wherein the instructions to cause the one or more processors to identify a ROI comprise instructions to cause the one or more processors to:
 receive an input indicative of an area of a touch-sensitive display of an image capture device; 
 transform the indicated area of the touch-sensitive display to a corresponding area of the pre-image; and 
 identify the corresponding area of the pre-image as the ROI. 
 
     
     
       19. The non-transitory program storage device of  claim 18 , wherein the instructions to cause the one or more processors to obtain a second image comprise instructions to cause the one or more processors to capture the second image using the image sensor in response to an input from an image capture control of the image capture device.